This invention relates to the deposition of metal films, and in particular to chemical vapor deposition of transition metals such as Fe, Ni, Ti, V, Cr, Fe, Ru, Os, Zr, W, Mo, Hf and Nb, for example. The invention more particularly concerned with deposition processes where an organometallic precursor such as a metallocene is employed.
Chemical vapor deposition of metals by thermal decomposition of a metal cyclopentadienyl precursor is described, for example, in U.S. Pat. Nos. 4,880,670; 4,882,206; 4,915988 and 4,992,305.
Cyclopentadienyl involves a five-carbon ring, and can form a bond with certain metals and metalloids. Under high temperature conditions (600.degree. C. to 1000.degree. C.) These compounds will decompose to deposit a metal film. The remaining organic residues are carried away in the vapor flow, so there is only a minor incorporation of carbon in the deposited metal. Some of these cyclopentadienyl compounds are attractive as precursors because they have a significant vapor pressure (0.1 Torr) at temperatures on the order of 100.degree. C., and are thermally stable over a generous range of temperatures.
Typically, these precursors are heated to produce vapor which is combined with a carrier gas entering a deposition chamber. The carrier gas and entrained organometallic vapor are flowed past a substrate. The substrate is heated to a suitable decomposition temperature so that the organometallic vapors decompose, leaving the metal film on the heated substrate. The decomposition temperature depends on the precursor used.
The metal cyclopentadienyl complexes employed in the techniques of the patents mentioned just above tend to have a higher than desired decomposition temperature in many cases, and are typically not subject to photolytic decomposition. This latter drawback makes laser writing of metal film patterns extremely difficult or impossible. Photo-assisted deposition, for selective area epitaxy, is also difficult or impossible with this technique. Precursors which involve cyclopentadienyl complexes are available for only a limited number of transition metals.
On the other hand, it is frequently desirable or necessary to carry out chemical vapor deposition at a lower temperature than can be used with this technique, to employ photolytic techniques, or to lay down a binary metal layer (more than one metallic element). It is desirable to have the flexibility of selecting among a wide range of metallic films without significantly modifying the deposition methodology involved. It is also desirable for the organometallic precursors to be stable and handleable materials, i.e., with low toxicity and minimal associated environmental problems.